i want to delete a part of a pdf document, how do i go about that?

i want to delete a part of a pdf document. how do i go about that? it's no text i want to erase, it's a whole area i want to delete (not the whole page).

i use acrobat x pro. when i go to tools, pages, crop, then double click and then ok, it deletes everything but the area that i cropped. i want to do the opposite. i want to delete the area that i selected.